1. Field of the Invention
The present invention relates to a magnetic barrel finishing machine capable of generating multiple different flows of abrasive by changing a magnetic field thereof so as to uniformly finish the workpieces.
2. Description of the Prior Art
There has been known a metal finishing machine characterized by regularly arranged permanent magnets on a non-magnetic disk. The known machine changes the magnetic field by rotation of the disk, allowing abrasives and free workpieces in a container to flow in the circumferential direction, thereby finishing the free workpieces (Examined Japanese Patent Publication No. HEI 4-26981, and Unexamined Japanese Patent Publication No. SHO 60-118466).
When a container filled with workpieces to be finished is placed at a central portion of the non-magnetic rotary disk, the workpieces tend to be finished unevenly, and therefore extra time is required until the finishing process is completed. Moreover, since the poles of the magnets are arranged in the order of N,S:N,S, an alternating magnetic field is generated in the circumferential direction. This regular arrangement of the poles may produce flows of abrasives repeatedly but regularly, and in some cases this causes irregular finishing of the workpieces or requires a lot of time for completion of the finishing process. Additionally, in the case of using a non-magnetic disk, there is a disadvantage in generating magnetic loss.
For example, as shown in FIG. 7 or 8, the conventional regular arrangement of poles such as N, S, N, S generates flows of abrasives along the same circumference (as shown by arrow 21 and loop 22).
Accordingly, a container 23 which contains workpieces and media (such as magnetic materials, abrasives, or compounds) must be disposed within a magnetic zone 24 (see FIG. 9). It is apparent that since the magnetic zone 24 is formed in a doughnut shape, the diameter of the container 23 must be set at a value 1/2 or less the diameter of a rotary disk 25.
In the case where the diameter of the container 23 is substantially equal to that of the rotary disk 25, a loop 22 is not generated at a central portion 26 as shown in FIG. 8, so that the workpieces at the central portion 26 are insufficiently finished, which leads to uneven finishing of the workpieces as a whole. To cope with this problem, a cylindrical body is sometimes put at the central portion of the container 23.